I have an 88 Malibu Sunsetter and the lag bolts that hold the motor mounts to the stringers have become loose due to a little rot around them. A local shop filled the holes with a white rubbery solution, but they continue to backout a small bit when I go out on the water. I can screw them back down, but they never tighten, just screw back down. What suggestions do you guys have about what I need to do or have the shop due to make a permanent fix for this? Any suggestions?

-Read instructions on product packaging. Drill a slightly oversized hole, slightly shorter than the new fastener, to remove any soft or deteriorated material. Clean debris from the hole. Apply a little penetrating oil or a silicone spray (like WD-40) to the new fastener to act as a release agent; wipe off excess film. Mix Marine-Tex White or Gray and fill the hole 3/4ths deep. Apply a small amount of Marine Tex to the fastener, being sure to fill in around the threads. With a slight twisting motion, insert the fastener in to the hole and allow the epoxy to cure for the full 24 hours. Marine-Tex will have the threads cast into it, and the fastener can be backed out if necessary. A wrench or a screwdriver with a little extra elbow grease may be needed the very first time the re-inserted fastener is removed since it will stick the first time it is backed out.

Although I've never done it myself, it seems like an adventure to replace the stringers. You can do it yourself and save probably $1000 in labor. Materials are about that much as well (depends on if you're going to re-foam the floor or not- search Correctcraftfan.com for more info- Weeding the pumkin patch is the name of one of the best threads, I think).

P.S. Do it as soon as you have the time- as they get weaker, you'll eventually get to the point that the hull is flexing so much it will throw your alignment out the window and you could get cracks in the gel. No joke.

I've done the stringer repair before on another boat and i can tell that at least in my case the stringers are pretty solid it's just that a few of the lag bolt are stripped out. Probably from the engine being taken out and put back in when it was being rebuilt. so i'm going to do the Marine tex fix. I've used the stuff before in another application and it is some beefy stuff.

If you find rot in one place there is almost always more and the fillers and glues are stop gap measures. Another work around is to lift the engine and put some sturdy angled steel to go over the stringers in engine area and you can tie in new mounts to the angled steel, assuming you can screw into some 'fresh' stringer near the original mounts. Only true fix is to gut the boat and replace stringers as mentioned.

I've used Marine Tex a lot and it's great for stuff like gelcoat scrapes and stripped trim screws. I would be very surprised if Marine Tex themselves would recommend it for motor mount bolts. That is a stop gap measure at best IMO.

Wood rot is like rust and cancer - you can't spot-treat it. Thru-bolting through long pieces of heavy angle iron would be a decent band-aid, but it should still be done right over the winter or something.